This invention relates to the pneumatic conveyance of materials and, in particular, to improved apparatus for introducing fluent bulk materials into a pneumatic conveying line.
In the pneumatic conveyance of various bulk materials it is well known to provide a hopper or similar collecting arrangement which supplies the bulk material to a feed tube. The feed tube in turn is provided with a suitable means, such as a feed auger, which advances the bulk material along the feeding tube and into some form of chamber through which a current of air is passed by way of air inlet and air outlet lines connected to that chamber. The bulk material which is deposited within the chamber is intended to be fluidized by the air current and carried by the air current through the air line outlet and along the outlet conveying line to a storage site, such as a silo.
In order to prevent air blow-back through the feed tube and alongside the auger, the outlet end of the feed tube is provided with a gate or other suitable one way valve arrangement which is intended to close when the flow of bulk material into the chamber slows down or stops thereby to prevent air blow-back through the feed tube and feed hopper. If blow-back occurs, the bulk material being handled may be sprayed around thus creating a potential hazard and, at least, a substantial cleanup problem.
The prior art has provided various devices of the nature indicated above as exemplified generally by the following U.S. Pat. Nos.:
______________________________________ 560,381 - Wainwright et al May 19, 1896 3,106,428 - Lenhart Oct. 8, 1963 3,460,869 - Herr Aug. 12, 1969 3,588,180 - Herr June 28, 1971 ______________________________________
One notable problem with all or virtually all of the prior art devices is that they were prone to a build-up of the material on or adjacent to the movable gate. After a period of time the gate would not close properly thus creating a substantial blow-back problem. Many of the prior art units were also prone to plugging thus requiring substantial down-time to partially dismantle the device and to remove the plugged up material.
Part of the problem with many of the prior art designs is that the internal configuration in the region of the gate is such that inadequate fluidization of many materials does not take place thus resulting in the build-up of deposits which eventually render the apparatus inoperative. In addition, no means were provided whereby the operator could observe the action occurring in the vicinity of the gate and take appropriate remedial action before plugging or blow-back occurred.
Another problem inherent in many or all of the prior art devices is that they are not sufficiently versatile. Most of them were designed for either only one or a very small number of very similar products. If an attempt is made to use them with products having substantially different characteristics, problems resulting from gate deposit build-up, plugging, and blow-back back soon arise.
Another problem inherent in most, if not all, of the prior art devices of the type under consideration is that they are only intended to be used in one fixed location. This necessitates the use of highly specialized and relatively expensive equipment for transporting dry bulk materials. In the past these dry bulk materials have been transported by pneumatic trailers and a relatively small number of specially designed rail cars. In the case of the so-called pneumatic trailers (which are intended for highway use), the entire vessel or container is pressurized during the unloading operation and this necessitates an extremely expensive structure. This, in turn, tends to increase shipping costs. Because of the specialized nature of the container, the pneumatic trailer is generally only usable one way thus meaning that the return trip is made with no load. This again keeps shipping costs high. Various fluent bulk materials, such as cement, lime, sand, salt and various dry chemicals, are commonly carried in this fashion.